*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}
body{
    background-color: darkslategray;
    display: flex;
    justify-content: center;
}
.a{
    width: 900px;
    height: 300px;
    position: relative;
    top: 200px;
    overflow: hidden;
    display: flex;
    justify-content: center;
}
.b{
    transition: .7s;
    overflow: hidden;
    /* border-top-left-radius: 15px;
    border-bottom-left-radius: 15px; */
    border-radius: 15px;

}
.b:hover{
    flex-shrink: 0;
    flex-grow: 0;
}
img{
    width: 400px;
    height: 100%;
}


